One type of paint sprayers or coating devices relies on a spinning bell-cup atomizer to atomize paint or coating material. The bell-cup atomizer generally needs to be spun at a relatively high RPM, to about 40,000 RPM so that its centrifugal force can atomize the coating material into a fine mist. Air is supplied through a shroud concentrically positioned over the bell-cup atomizer, adjacent where the atomized coating material leaves the bell-cup atomizer, to direct the atomized coating material to an object to be coated. The shroud is typically connected to an injection manifold, which supplies compressed air to the shroud and the coating material to the bell-cup atomizer. In practice, the atomized coating material adheres to the shroud and clogs the air holes, necessitating frequent cleaning.
To clean the air holes of a conventional shroud, one must first remove the bell-cup atomizer from a turbine shaft, which rotates the same, to remove the shroud from the manifold. Moreover, cleaning may require probing the air holes with pins or the like, which can undesirably change or distort the hole size. The hole distortion can alter the pressure, velocity, and other characteristics of the shaping air, which can generate inconsistent air streams. If the holes are successfully cleaned, the shroud is reattached to the manifold and the bell reattached to the turbine. This process is very time consuming. Further, when removing the shroud, O-rings frequently fall off the paint injection manifold, and must be replaced. This requirement adds additional cost to the operation.
In this regard, U.S. Pat. No. 4,997,921 issued to Weinstein and 4,601,921 to Lee disclose a two-piece shroud that does not require removal of the bell-cup atomizer to clean the shroud air holes. The two-piece shroud has an annular outer ring positioned concentrically over an annular inner ring. The outer ring is separable from the inner ring so that the outer ring can be detached from the injection manifold without disturbing the bell-cup atomizer or the inner ring. The two-piece shroud, however, does not have a plurality of individual shaping air holes at its distal end. Lee provides a single annular opening at its distal end. Weinstein has air holes near its distal end, but air exits at its distal end also through a single annular opening, where the individual air streams merge and exit the shroud as a single air stream. As air does not exit from individual air holes or nozzles, the air shaping capability is reduced.
Accordingly, there is a need for a shroud that provides an effective air shaping capability and easy access to the air holes or nozzles for cleaning. The present invention meets this need.